1. Field of the Invention
This invention relates generally to magnetoresistive random access memory (MRAM) devices and, more particularly, to an MRAM memory element structure.
2. Description of the Related Art
Integrated circuit designers have always sought the ideal semiconductor memory: a device that is randomly accessible, can be written or read very quickly, is non-volatile, but indefinitely alterable, and consumes little power. Magnetoresistive random access memory (MRAM) technology has been increasingly viewed as offering all these advantages.
A magnetic memory element has a structure which includes ferromagnetic layers separated by a non-magnetic barrier layer that forms a tunnel junction. Information can be stored as a digital xe2x80x9c1xe2x80x9d or a xe2x80x9c0xe2x80x9d as directions of magnetization vectors in these ferromagnetic layers. Magnetic vectors in one ferromagnetic layer are magnetically fixed or pinned, while the magnetic vectors of the other ferromagnetic layer are not fixed so that the magnetization direction is free to switch between xe2x80x9cparallelxe2x80x9d and xe2x80x9cantiparallelxe2x80x9d states relative to the pinned layer. This latter ferromagnetic layer is called a xe2x80x9csensexe2x80x9d layer. In response to parallel and antiparallel states, the magnetic memory element represents two different resistance states, which are read by the memory circuit as either a xe2x80x9c1xe2x80x9d or a xe2x80x9c0.xe2x80x9d It is the detection of these resistance states for the different magnetic orientations that allows the MRAM to read information.
Unfortunately, the ability of the memory device to reliably switch states is adversely affected by magnetic coupling between the sense and pinned layers. Magnetic coupling between the sense layer and the pinned layer results in the sense layer being biased toward one magnetic orientation producing a magnetic field offset in the magnetic field required for switching the sense layer during programming. In addition, known MRAM elements may exhibit electrical shorting between the sense layer and the pinned layer through a conductive side wall film which may form during etching to define memory elements. This reduces device yields.
It would be desirable to have an MRAM element with reduced magnetic coupling between the sense and pinned layers and reduced electrical shorting.
This invention provides an MRAM element which utilizes sense and pinned ferromagnetic layers of different sizes. This reduces magnetic coupling between the sense and pinned layers, and additionally decreases the chance of an electrical short occurring between the layers during device fabrication. This invention also discloses a method for fabricating an MRAM element with sense and pinned layers of different sizes. These and other advantages and features of the invention will be more completely understood from the following detailed description of the invention which is provided in connection with the accompanying drawings.